Means for limiting the acceleration of machine elements



Jan. 26, 1943. K, J. J. MCGOWAN 2,30 52 MEANS FOR LIMITING THE ACCELERATION OF MACHINE ELEMENTS 'Filed Aug. 20, 1941 'INVENTOR Patented Jan. 26, 1943 UNITED STATES iATiENT OFFICE MEANS FOR LHHITING THE ACCELERATION OF MACHINE ELEMENTS Application August 20, 1941, Serial No. 407,594

2 Claims.

My invention relates to means for limiting the acceleration of machine elements.

In railway switch operating apparatus of the type which includes a hand lever for throwing a spring switch, it sometimes becomes necessary or desirable to reverse the position of the switch throwing device .by the hand throw lever when the switch points occupy positions out of agreement with the position of the switch throwing device. When this is done, the spring of the usual spring biasing means is compressed to a greater extent than is normally the case when the switch is reversed by means of the hand throw lever, and the resultant releasing of the force stored in the spring biasing means tends to jerk the hand throw lever out of the operators hand. One object of my present invention is to provide means for preventing this from happening to guard against possible injury to the operator.

According to my invention, I provide an inertia brake for the hand throw lever having brake shoes biased by springs to non-braking positions and connected by levers with the hand throw lever in such manner that during normal operation of the switch by the hand throw lever no braking effort takes place, but that, if a large accelerating force is applied to the hand lever for any reason, this accelerating force will cause the brake shoes to move to braking positions and thus apply a friction load to the hand throw lever which opposes the accelerating force on the lever.

Other objects and characteristic features of my invention will become apparent as the description proceeds.

I shall describe one form of apparatus embodying my invention, and shall then point out the novel features thereof in claims.

In the accompanying drawing, Fig. l. is a diagrammatic View showing a spring switch A operated by a switch operating mechanism B to which my invention is applicable, Fig. 2 is a top plan view showing an inertia brake embodying my invention applied to the shaft 3| to which the hand throw lever of the mechanism shown in Fig. 1 is attached. Figs. 3 and 4 are sectional views of the brake shown in Fig. 2 taken substantially on the lines III-III and IV--IV of Fig. 2.

Similar reference characters refer to similar parts in each of the several views.

Referring first to Fig. 1, the reference character A designates a railway switch comprising, as usual, two fixed rails l and la and two movable rails 2 and 2a. The movable rails are fastened together by a front rod 5, a head rod 6 and a tie rod 8, and may be moved into a normal or a reverse position by means of a switch operating mechanism B which is connected with the head rod 6 through the medium of an operating rod 9 and a spring connecting rod C. When the switch occupies its normal position in which it is shown in Fig. 1, the movable rail 2 engages the fixed rail i and the movable rail 2a is spaced a slight from the rail la. When th switch is reversed, however, the movable rail 2a then engages the fixed rail la, and the movable rail 2 is spaced from the fixed rail 1 The spring connecting rod C may have any desired construction which will cause the switch points to be held in whichever extreme position .they are moved to by the mechanism B with surficient force to permit facing point moves over the switch without danger of displacement of the switch points, but which will yield when the train trails the switch, and thereby allow the train to force the switch points to positions opposite to their initially set positions. One form of spring connecting rod which will accomplish the necessary result is shown and described in Letters Patent of the United States No, 1,976,827 granted to Herbert L. Bone on October 16, 1934, for Railway switch operating apparatus.

The switch operating mechanism B may, for example, be similar to that shown and described in the said Bone Patent No. 1,976,827 just referred to, and the various parts are designated in the drawing by the same reference characters as they are designated by in the patent. t is believed, therefore, that for purposes of my present invention, the following brief description of this mechanism will sui'fice.

The mechanism B includes a motion plate 26 which is arranged to be reciprocated between two extreme positions by means of a hand lever through the med um of a shaft 55 and a gear wheel 33: Formed in the motion plate is a cam slot 28 provided with offset end portions which extend parallel to the direction of motion of the motion plate, and with an intermediate connecting portion which extends at an angle to the direction of motion of the motion plate, this slot cooperates with a roller 34 operatively connected with the operating rod 9 in such manner that the switch will be moved to its normal or to its reverse position according as the motion plate occupies the extreme position shown, or its opposite extreme position. The mechanism also includes a locking plunger 39c which cooperates With a pair of aligned notches d8 in a lock rod L secured to the front rod 5 of the switch A. The locking plunger is biased by means of a spring 3911 to a locking position in which, when the switch occupies its normal position, it will enter the notches it in the lock rod L and thus lock the switch in its normal position, but the locking plunger is arranged to be moved to an unlocking position, prior to any movement of the switch points away from their normal positions by the mechanism 33, by suitable means indicated diagrammatically in the drawing by a lug 42 provided on the motion plate and cooperating with a lug 3901 provided on the locking plunger. The locking plunger is also arranged to be moved to its unlocking position, prior to any movement of the switch points away from their normal positions by a trailing train, through the medium of suitable lock releasing linkage including a bell crank lever 5i, substantially as described in the said Bone Patent No. 1,976,827 referred to hereinbefore.

With the switch A arranged to be operated in the manner described it may happen that an operator will attempt to operate the mechanism B when the switch points occupy positions out of agreement with the position of the mechanism. For example, an operator may operate the mechanism B when the parts of the mechanism occupy their normal positions in which they are shown in the drawing and the switch points are held in their trailed positions by the wheels of a train which has stopped on the switch. When this happens, the operation of the mechanism releases the energy stored in the compressed spring of the spring connecting rod C, and causes this energy to be transmitted back through the operating rod 9, roller 34, and an inclined portion of the cam slot 28 to the motion plate 25, and from thence through the gear Wheel and shaft 3! to the hand lever 38, with the result that the hand lever 3D is rotated very suddenly in a counterclockwise direction as viewed in Fig. i. This sudden rotation of the hand lever tends to jerk the hand lever out of the operators hand, thereby creating a dangerous condition, and in some instances causing damage to the apparatus. In accordance with my present invention, I provide an inertia brake which I shall now describe for opposing rapid rotation of the shaft 3! due to energy stored in the spring, under the conditions above described.

Referring now to Figs. 2 to 4, inclusive, my inertia brake in the form here illustrated comprises a circular housing 68 which is secured by means of studs iii to the one side of the main casing it of the mechanism B in concentric relation to the shaft 3!. The housing 60 acts as a stationary brake drum, and cooperates with two semicircular brake shoes 52. The brake shoes 62 are provided at their opposite sides with flanges (it, and are biased toward each other to non-braking positions by means of biasing springs 54 disposed within aligned slots 65 formed in the outer sides of the flanges 63. The brake shoes are also provided at the inner sides of their adjoining ends with transversely extending mating recesses 68 which receive the outer ends of a pair of brake levers 6 1. The opposite sides of the brake levers extend into recesses 68 provided in an operating member 69 which is mounted on the shaft 3| to rotate therewith. The housing 6i] is closed at its outer end by a cover plate It! which positions the parts lengthwise within the housing.

The parts are so proportioned that when the switch operating apparatus is operated by the hand lever in the usual manner, the accelerating force which is transmitted from the shaft to the brake shoes 62 through the operating member 69 and the levers Bl will be insufficient to move the brake shoes away from their nonbraking positions in opposition to the bias of the springs 6 and under these conditions the brake shoes will rotate with the shaft Si without exerting any frictional force on the shaft. However, if a large accelerating force is applied to the shaft (ii, as will be the case if the hand lever is operated when the switch points initially occupy positions out of agreement with the position of the hand lever, the inertia of the brake shoes will tend to prevent their rapid acceleration by the lever $6, and under these latter conditions the lever 66 will be rotated by the operating member 69 to positions in which they act to force the brake shoes to their braking positions. It will be obvious that when the brake shoes occupy their braking positions, the frictional force which is developed between them and the housing 60 will apply a friction load to the shaft 3! which opposes the acceleration of the shaft. The parts are further so proportioned that this load will be sufficient to limit the acceleration of the shaft to a value which is insufficient to jerk the hand throw lever out of the operator's hand.

One advantage of an inertia brake embodying my invention is that it is inexpensive to manufacture and maintain.

Another advantage of an inertia brake emb-odying my invention is that it can be installed on switch operating mechanisms which already in service.

Although I have herein shown and described only one form of apparatus embodying my invention, it is understood that various changes and modifications may be made therein within the scope of the appended claims without departing from the spirit and scope of my invention.

Having thus described my invention, what I claim is:

1. An inertia brake for limiting the acceleration of a machine element comprising a circular housing which acts as a brake drum, a plurality of brake shoes disposed within said brake drum and biased by means of springs to non-braking positions, each said brake shoe being provided at each end with a recess which mates with the corresponding recess in the contiguous end of the other brake shoe, an operating member operatively connected with said machine element and provided with recesses which are disposed opposite the mating recesses in said brake shoes, and a plurality of levers each having one end disposed in a difierent one of the recesses in said operating member and the other end disposed in the aligned recesses in said brake slices, the parts being so proportioned that said springs will hold said brake shoes in their non-braking positions when sand element is accelerated at any rate which is less than a predetermined rate but i if the rate of acceleration of said element exc: predetermined rate the iner a of the bi he shoes will cause said operating r:

.. o to rotate said levers to positions in which the lovers act to force said brake shoes to braking positions to thereby limit the acceleration of said 2. The combination with a shaft which is normally rotated in one direction or the other at a relatively slow rate but which is connected with means which tends to at times rapidly accelerate said shaft, of an inertia brake for limiting the acceleration of said shaft, said brake comprising a fixed circular housing surrounding said shaft in concentric relation thereto and acting as a brake drum, two semicircular brake shoes disposed within said brake drum and biased by means of springs to non-braking positions, each said brake shoe being provided at its ends with a recess which mates with the corresponding recess in the contiguous end of the other brake shoe, an operating member mounted on said shaft to rotate therewith within said brake shoes and provided with two diametrically opposite recesses disposed opposite the mating recesses in said brake shoes, and two levers each having one end disposed in a different one of the recesses in said operating member and the other end disposed in the aligned recesses in said brake sh'oes, the parts being so' proportioned that said levers will move said brake shoes to their brake positions in opposition to the bias of said springs when and only when said shaft is rapidly accelerated to thereby limit the acceleration of said shaft.

KENNETH J. J. MCGOWAN. 

